Continuous carbon filament production

ABSTRACT

A PROCESS FOR THE PRODUCTION OF CARBON FILAMENTS WHICH COMPRISES FEEDING ORGANIC FILAMENTARY MATERIAL, PREFERABLY POLYCARYLONITRILE FILAMENTARY MATERIAL, OR SUCH MATERIAL WHICH HAS ALREADY BEEN SUBJECTED TO A PRIOR HEAT TREATMENT, CONTINUOUSLY IN A SERIES OF PASSES THROUGH A LEAST ONE HEAT TREATMENT ZONE IN WHICH THE TEMPERATURE INCREASES AS THE FILAMENTARY MATERIAL TRAVERSES THE SUCCESSIVE PASSES WHILE THE DIRECTION OF TRAVEL OF THE FILAMENTARY MATERIAL IN EACH PASS IS SUBSTANTIALLY AT RIGHT ANGLES TO THE DIRECTION OF INCREASING TEMPERATURE.

March 2, 1971 V B. A. TOWNSEND 3,557,330

CONTINUOUS CARBON FILAMENT PRODUCTION Filed Aug. 26, I968 2 Sheets-Sheet 1 INVENTOR Bruce Arnold Townsend Davis, Hoxie, Faithfull 8g ATT 1 I B.A. TOWNSEND i CONTINUOUS CARBON FIL-AMENT PRODUCTION Filed Aug. 26, 1968 2 Sheets-Sheet 1 away imam ' wvtzwvk Bruce Arriold Townsend 4 Davis, HOXiG, Faithfull 8c Hapg'ood United States Patent 3,567,380 CONTINUOUS CARBON FILAMENT PRODUCTION Bruce Arnold Townsend, Rugby, England, assignor to Courtaulds Limited, London, England Filed Aug. 26, 1968, Ser. No. 755,262

Int. Cl. C011) 31/07 U.S. Cl. 2 3--209.1 11 Claims ABSTRACT OF THE DISCLOSURE A process for the production of carbon filaments which comprises feeding organic filamentary material, preferably polycarylonitrile filamentary material, or such material which has already been subjected to a prior heat treatment, continuously in a series of passes through a least one heat treatment zone in which the temperature increases as the filamentary material traverses the successive passes while the direction of travel of the filamentary material in each pass is substantially at right angles to the direction of increasing temperature.

This invention relates to a process for the production of filamentary materials and in particular to an improvement in processes for the continuous production of filament of carbon.

Carbon filaments may be produced by subjecting organic filamentary material to specific conditions of temperature and surrounding atmosphere. Thus, in a first stage, the filaments may be heated to a temperature in the range from about 200 C. to 300 C. in an atmosphere of air, air enriched with oxygen or nitrogen, and they may then be heated at a temperature in excess of 1000 C. in an inert atmosphere. If graphtised filaments are to be produced further heat treatment is necessary which takes place at a temperature which is higher than 2000 C., also in an inert atmosphere.

In the continuous production of carbon filaments these heat treatments require to be carried out in succession, preferably on continuously moving filamentary material. Since each treatment may take several hours the production of continuous filaments in this manner is very slow. It is an object of this invention to enable the continuous production of carbon filaments to take place at an increased rate.

According to the invention a process for the production of carbon filaments comprises feeding organic filamentary material or such material which has already been subjected to a prior heat treatment continuously in a series of passes through at least one heat treatment zone in which the temperaure increases as the filamentary material in each pass is substantially at right angles to the direction of increasing temperature.

In the process of the invention one or more ends of organic filamentary material may be employed, the filamentary material being fed to the heat treatment zone at a suitable temperature. Thus, for example, the first stage treatment may be carried out by heating organic filamentary material slowly to a temperature of 200 C. to 300 C. in air, air enriched with oxygen or nitrogen, at Which temperature it may be maintained for a period of from half an hour to four hours. The later stages may be carried out in an inert atmosphere at the higher temperatures. In one form of the invention using one pair of advancing rollers within a heating zone, a single continuous filament may be threaded round a pair of thread storing and thread advancing rollers within the zone, the inlet section of which is maintained at a temperature within the required lower range. If the organic filaments are introduced to the process without prior heat treatment the atmosphere 3,567,380 Patented Mar. 2, 1971 ice at this point may be air, air enriched with oxygen or nitrogen. If the atmosphere contains oxygen, only the first stage heat treatment may be carried out in this zone, and the temperature of the zone at the outlet end may suitably be in the vicinity of 300 C. If however the first stage heat treatment is carried out in an inert atmosphere it may be possible to continue the increase of temperature to that at which carbonisation takes place in the same heat treatment zone provided that adequate measures for removal of the gaseous decomposition products are taken. It may in any case be preferred to separate this stage of the treatment entirely from the carbonising stage.

In another form of the invention, also applicable to the to the first stage of production of carbon filaments, as well as to the later stages a number of ends of organic filamentary material are fed in parallel around a series of rollers disposed across the band of filaments to produce a number of passes for the filaments during their passage through the heat treatment zone.

In a preferred form of the invention filaments which have been subjected to the first stage heat treatment are fed continuously to a heat treatment zone the cool end of which is mainained at a temperature substantially equal to that at which the first stage heat treatment was completed, for example about 300 C. The filaments advance through the heat treatment zone in an inert atmosphere, and their temperature is progressively increased as they travel through the zone until they reach a temperature of at least 1000 C. They are maintained at such a temperature for a sutficiently long time to complete their carbonisation. This process may take for example from about half an hour to four hours. If desired the temperature may be further increased within the same heat treatment zone to about 2000 C. at which temperature the filaments may be maintained during their passage through the zone for sufficient time to graphitise them. This period may also be in the range from about half an hour to four hours, and the atmosphere is again inert. Preferably the graphitisation temperature is at least 2500 C. In this form of the invention the filament may for example be advanced through the heat treatment zone in either of the ways described above, or in any other suitable manner. If desired two separate heat treatment zones may be employed for thee arbonisation stage and the graphitisation stage respectively.

In the process of the invention it may be desirable to provide the heat treatment zone or zones with a number of baffles across the direction of advance of the filaments. Such bafiies minimise contamination of the filaments in the later stages of the process from waste gases formed in the earlier stages, and also enable closer control of temperature conditions to be maintained in the various parts of the heat treatment zone. The rollers employed may be disposed outside the heat treatment zone or more preferably Within it and at least for use in the high temperature stages may most suitably be made of carbon. Any suitable method of heating the heat treatment zone may be employed, using for example regenerative methods of combustion, but it is preferred to use electrical heating. Suitable types of heating include conventional electric furnaces, induction heating and dielectric heating. The organic filaments used in the process may for example be cellulosic polyamide or polyester filaments, or any other type of filaments the structure of which contains a carbon to carbon backbone, but preferably consist wholly or mainly of polyacrylonitrile. Carbonised or graphitised fibres produced by the process of the invention can be made of any desired length, and are substantially free from bends or kinks.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view, with parts broken away to reveal the underlying structure, of a first embodiment of apparatus for carrying out the process according to the invention, and

FIG. 2 is a similar view of a second embodiment of apparatus for carrying out the process according to the invention.

FIG. 1 shows a furnace having a base 1, side walls 2, 3, end walls 4, 5 (only one of which is shown in detail) and a cover 6.

Mounted within the furnace is a thread-storing and thread-advancing device formed by two rollers 7, 8, made for example of carbon which are rotatably mounted at their ends in the end walls 4, 5 of the furnace. The roller 8 is positively driven in the direction of the arrow A by any suitable drive means 9 disposed externally of the furnace.

The axes of the rollers 7 and 8 are not parallel to one another, but are slightly inclined to one another. If a continuous filament 10 of organic material is wrapped around the rollers 7 and 8, as shown in FIG. 1, the turns of the filament will progress along the rollers in the direction of the arrow B when the roller 8 is driven. The roller 7 may be an idler roller or it too may be positively driven by suitable drive means (not shown) disposed externally of the furnace.

The furnace is divided into a plurality of compartments 11a, 11b, 11c and l ld by bafiles 12 shown schematically in FIG. 1. These bafiles are disposed parallel to the end walls 4, 5 and are provided with suitable apertures to allow the rollers 7, 8 to pass therethrough.

The furnace is heated by any suitable form of electrical heating means, for example a plurality of resistance heating elements arranged substantially parallel to the rollers 7 and 8. One such heating element is shown in FIG. 1 and is designated by the numeral 13. These heating elements are so dimensioned and/or disposed in the furnace that as the turns of the filament 10 pass along the rollers 7, 8 in the direction of the arrow B they pass through zones of increasingly high temperature. Thus the compartment l lb is hotter than the compartment 11a but cooler than the compartment 11c, and the compartment 11a is hotter than the compartment 11c.

When the above described furnace is used to carry out the first stage heat treatment or organic filamentary material in the production of carbon filaments, the continuous filament 10 (which may be, for example, a polyacrylonitrile filament) is led through an aperture 14 in the side wall 2 into the compartment 11a which is maintained at a temperature of approximately 200 C. After passing along the rollers 7, 8 in a plurality of turns, the filament 10 leaves the compartment 11b through an aperture 15 in the side wall 3. The compartments 11b, 11c and 11d are maintained at temperatures of approximately 235, 270 and 300 C., respectively. The residence time of the filamentary material in the final compartment 11d should be at least /z hour. The furnace atmosphere may be air, in which case no special provision need be made to supply an artificial atmosphere to the furnace. If, however, it is desired to heat the filament 10 in an atmosphere of air enriched with oxygen, or in nitrogen, the gas in question may be fed to the frnace via a pipe 16 passing through the end wall 4. The gas supplied via the pipe 16 may be preheated to approximately 200 C. in any suit able manner. Gas, including products evolved from the filamentary material during the heat treatment, may be withdrawn from the furnace via pipes 17 passing through the cover 6 and/ or the end wall 5.

The furnace shown in FIG. 1 may also be employed for the carbonisation of filamentary material which has already been subjected to a first stage heat treatment at a temperature of from 200 to 300 C. In this case, the compartments 11a, 11b, 11c and 11d are maintained at temperatures of approximately 300, 550, 800 and 1000 C., respectively. The residence time of the filamentary material in the final compartment 1'1d should be at least /2 hour. This carbonisation treatment is performed with an inert atmosphere in the furnace, supplied via the pipe 16.

The carbonised filaments, may if desired, be graphitised in athird heat treatment stage at a temperature of at least 2000 C. This treatment may be performed in the same furnace as that in which the second heat treatment stage is performed. In this case the filamentary material should reside for at least /2 hour in the final compartment of the furnace, which compartment is maintained at a temperature of, for example, 2500 C. Alternatively, the graphitisation stage of the process may be performed in a different furnace from that in which the carbonisation of the filaments is performed.

Although the above description of the furnace shown in FIG. 1 refers to the treatment of a single filament 10 in the furnace, it will be appreciated that a bundle of filaments may be passed through the furnace by the rollers 7, 8.

FIG. 2 shows a furnace for treating a plurality of filaments 20 simultaneously. The furnace body is shown very schematically in chain lines and is designated general ly by the numeral 21. The furnace comprises side walls 22, 23, end walls 24, 25, a top 26 and a base 27.

A set of spaced-apart, parallel rollers 28, made for example of carbon, with their axes vertical are disposed inside the furnace adjacent to the side wall 22. A second set of spaced-apart parallel rollers 29, which may also be made of carbon, with their axes vertical are disposed inside the furnace adjacent to the side wall 23. The rollers 29 are driven rollers. To this end, each roller 29 has a wormwheel 30 keyed to the lower end of its spindle 31. The wormwheels 30 of all the rollers mesh with worms 32 keyed to a common shaft 33 which is driven by a motor 34. These driving arrangements for the rollers 29 are disposed externally of the furnace. The rollers 28 may be idler rollers, these rollers being mounted for rotation in bearings (not shown) in the top 26 and the base 27 of the furnace.

The filaments 20 are led into the furnace through an aperture 35 in the side wall 22 and leave the furnace through an aperture 36 in the side wall 23. The furnace may be heated in the same way as the furnace of FIG. 1 and the interior of the furnace is divided into compartments 37a, 37b, 37c and 37d by means of baffles 38 disposed parallel to the end walls 24, 25. These baffles are secured to the side wall 22 intermediate adjacent rollers 28 and terminate short of the opposite side wall 23 adjacent to the rollers 29. As in the case of the furnace of FIG. 1, the temperatures of the compartments 37ad increase in the direction from the end wall 24 to the end wall 25.

The furnace described above with reference to FIG. 2 may be employed in substantially the same way as the furnace of FIG. 1 for the continuous production of carbonised or graphitised filaments. As in the case of the furnace of FIG. 1 the furnace of FIG. 2 would be provided with means (not shown) for establishing an inert atmosphere in the interior of the furnace.

What is claimed is:

1. In a process for the production of carbon filaments in which organic filamentary material is subjected to a first preliminary heat treatment at a temperature between about 200 C. and about 300 C. in an oxidizing atmosphere and is subsequently subjected to a second heat treatment at a temperature in excess of 1,000 C. in an insert atmosphere, the improvement which comprises carrying out said second heat treatment bp passing the filamentary material in a series of passes through a heat treatment zone in which the temperature increases as the filamentary material traverses the successive passes, the direction of travel of the filamentary material in each pass being substantially at right angles to the direction of increasing temperature in said zone.

2 In a process for the production of carbon filaments in which organic filamentary material is subjected to a first preliminary heat treatment at a temperature between about 200 C. and about 300 C. in an oxidizing atmosphere and is subsequently subjected to a second heat treatment at a temperature in excess of 1,000 C. in an inert atmosphere, the improvement which comprises carrying out said first and second heat treatments by passing the filamentary material in a series of passes through first and second heat treatment zones, the temperature in each zone increasing as the filamentary material traverses the successive passes, the direction of travel of the filamentary material in each pass in each zone being substantially at right angles to the direction of increasing temperature in that zone.

3. The process as claimed in claim 2 in which the organic filamentary material is heated in the first heat treatment zone to approximately 300 C. and maintained at that temperature for from /2 to 4 hours and is then heated in the second heat treatment zone from a temperature of approximately 300 C. to a temperature of approximately 1,000 C.

4. The process as claimed in claim 2, in which the filamentary material is maintained in said first zone at a temperature of approximately 300 C. for a period of from /2 hour to 4 hours.

5. The process as claimed in claim 3, in which the filamentary material is maintained in said second zone at a temperature of approximately 1000 C. for a period of from /2 hour to 4 hours.

6. The process as claimed in claim 3, in which the filamentary material is subsequently heated in a third heat treatment zone from a temperature of approximately 1000 C. to a temperature in excess of 2000 C.

7. The process as claimed in claim 6, in which the filamentary material is heated in the third heat treatment zone to a temperature of approximately 2500 C.

8. The process as claimed in claim 6*, in which the filamentary material is maintained in said third zone at a temperature in excess of 2000 C. for a period of from /2 hour to 4 hours.

9. The process as claimed in claim 1, in which a single filament or a plurality of filaments is advanced through the second heat treatment zone by a thread-storing threadadvancing device.

'10. The process as claimed in claim 1, in which a plurality of organic filaments are fed in parallel around a series of rollers disposed in the heat treatment zone 5 to produce a number of passes of the filaments in their passage through the heat treatment zone.

11. The process as claimed in claim 1, in which the organic filamentary material is polyacrplonitrile.

References Cited UNITED STATES PATENTS 3,053,775 9/1962 Abbott 252-421 3,011,981 12/1961 Soltes 252502 3,285,696 11/1966 Tsunoda 23209.1 3,427,120 2/ 1969 Shindo et al. 23209.1X

OTHER REFERENCES Carpenter Derwewt Belgian Patents Report, No.

30 53/67, Jan. 31, 1968, 2A, pp. 2-3.

EDWARD J. MEROS, Primary Examiner US. 01. Xrg. 2 -2094; 8-1155 

